The present invention relates to an exhaust-gas system for a vehicle having an internal combustion engine, including a Helmholtz resonator and two exhaust-gas lines extending towards the resonator.
Exhaust-gas systems for multi-cylinder, high-performance internal combustion engines are normally provided with two exhaust-gas systems separated from one another. Each originate, for example, from a cylinder bank of a V-type engine or, for example, also from two or three cylinders of a multi-cylinder in-line engine in each case.
The advantage of the configuration with separate exhaust-gas lines over a single exhaust-gas line with a large individual cross section is that it is easier to install, particularly due to the small amount of space available in a vehicle. Nevertheless, it provides sufficiently large cross sections for the exhaust-gas line.
In addition to a shared or also separate exhaust-gas catalytic converter, further components are installed in the exhaust-gas lines to reduce the combustion-related noise emissions from the internal combustion engine, such as, for example, front mufflers, mid-mufflers or also rear mufflers and, finally, the exhaust-gas lines also still each comprise end pipes or else exhaust-gas outlet openings.
It is already known in the art for selectively tuned Helmholtz resonators or λ/4 mufflers to be provided in the housing of the rear muffler or also connected to the rear muffler by a branch line. These resonators or mufflers are each tuned to a speed range of the internal combustion engine in which the internal combustion engine is inclined towards conspicuous droning frequencies that are inconsistent with the vehicle's comfort specifications. The aim is for these devices, which influence the noise emissions from the internal combustion engine, to selectively lower the opening level at the exhaust-gas outlet or the exhaust-gas outlet openings.
DE 200 03 666 U1 discloses a multi-stage Helmholtz resonator in which the resonator capacity can be increased or reduced via a switchable flap provided in the resonator housing, as a result of which a sound level reduction of two different main frequencies can be achieved.
DE 100 84 870 T1 discloses an exhaust-gas system for a vehicle which has a muffler that is coupled via a branch line to a Helmholtz resonator which is formed from a stand-alone resonator housing. The housing is arranged on the vehicle underside and does not have exhaust gas flowing through it and is formed from a polymer.
It is also already known in the art for switchable exhaust-gas flaps to be provided in the exhaust-gas system, said flaps further reducing noise emissions when they are closed, due to a resulting reduction in the cross section of the exhaust-gas lines that can be flowed through by the exhaust gas. However, the aforementioned measures regularly increase the exhaust-gas counter-pressure prevailing in the exhaust-gas system and consequently cause a deterioration in the responsiveness of the internal combustion engine experienced by the vehicle driver and increase the engine's fuel consumption due to the expulsion work that has to be done by the internal combustion engine against the high exhaust-gas counter-pressure.
Taking this as the starting point, the problem addressed by the present invention is that of creating an exhaust-gas system for a vehicle with an internal combustion engine, which exhaust-gas system allows a reduction in noise emissions from the internal combustion engine without, however, thereby generating a high exhaust-gas counter-pressure. A method for operating an exhaust-gas system of an internal combustion engine is also to be provided.
In order to solve this problem, there is provided an exhaust-gas system, and a method of operating same, in accordance with embodiments of the invention.
The invention creates an exhaust-gas system for a vehicle having an internal combustion engine, with a Helmholtz resonator and two exhaust-gas lines extending towards the resonator, wherein the resonator has two neck openings to a resonator volume. Each neck opening is coupled to one of the exhaust-gas lines, and the resonator is tuned for the damping of a dominant engine order.
The invention takes account of the cramped spatial conditions routinely found in a vehicle for sound damping and, rather than using the muffler capacity for the integration of damping components which allow sound damping according to the reflection method or absorption method, provides for the configuration of a Helmholtz resonator in a housing utilizing the possible sound-damping volume. The resonator volume (also referred to herein as resonator capacity) is coupled by means of a neck opening in each case with one of the exhaust-gas lines of the dual-flow exhaust-gas system.
Consequently, the exhaust-gas system comprises two exhaust-gas lines which are provided for the exhaust-gas line from the internal combustion engine towards the exhaust-gas outlet openings and each exhaust-gas line is coupled by means of a neck opening or branch line to the housing forming the resonator volume of the Helmholtz resonator and the Helmholtz resonator is tuned for the damping of at least one engine order specific to the internal combustion engine. The engine order in this case may be the one that makes the greatest contribution in quantitative terms to the opening level; the resonator may therefore be tuned to the frequency that contributes the greatest sound-pressure level in quantitative terms to a measured opening level. The resonator may, for example, be accurately tuned to the frequency that produces the highest level in a licensing run for type approval.
This opening level may therefore be the relevant opening level in the case of a licensing run for worldwide type approval for the vehicle, for example, said opening level then being reduced by means of the resonator to a permitted measured sound-pressure level, without this requiring sound-damping devices which work according to the reflection or absorption method. Due to the absence of sound-damping devices which work according to the reflection or absorption method, the disadvantage associated therewith of increasing the exhaust-gas counter-pressure in the exhaust-gas plant is also eliminated.
A development of the invention is provided in this case, in that the resonator comprises a housing exhibiting the resonator volume, which housing is configured separately from other component housings of the exhaust-gas system. The housing is arranged spaced apart from the rear region of the vehicle. This configuration means that within the framework of the installation space available for sound-damping measures on the vehicle, the largest possible resonator volume is used and the resonator housing is attached at a great distance from the rear region of the vehicle, as a result of which a component exhibiting a rigid structure, namely the housing required for sound damping, is removed from the region of the rear structure of the vehicle and if the rear of the vehicle is damaged by the rigid component, components on the vehicle which are no longer adjacent are damaged by the rigid component.
According to a development of the invention, it is also provided that the exhaust-gas system has a flap in each case arranged in the region between the exhaust-gas line and the resonator volume, which flap is configured for the at least partial opening and/or closing of the neck opening in each case. With these flaps arranged adjacent to the resonator volume, the Helmholtz resonator can be switched on or switched off, as it were. It is therefore possible to influence the sound level at the exhaust-gas outlet openings of the exhaust-gas lines. It is also possible to adjust the damping level of the resonator variably through an only partial opening of the neck openings. In this case, the resonance frequency of the damping does not change, but only the degree of damping corresponding to the opening angle of the flaps or resonator flaps.
The opening and/or closing of the flaps may take place in a speed-range-selective, gear-ratio-selective or driving-mode-selective manner. The flaps may, for example, be opened in a given speed range of the vehicle, so that the Helmholtz resonator reduces the opening level, while the flaps are closed in another speed range of the vehicle or, for example, in a sports driving mode of the vehicle and the opening level is therefore higher.
According to a development of the invention, it is also provided that each exhaust-gas line in the through-flow direction of the exhaust-gas lines downstream of the resonator has at least two exhaust-gas outlet openings and at least one exhaust-gas outlet opening in each case is provided with an exhaust-gas flap, by means of which the exhaust-gas outlet opening is reversibly closable.
This means, in other words, that each exhaust-gas line has two exhaust-gas outlet openings, so in the case of two exhaust-gas lines, four exhaust-gas outlet openings are provided, wherein an exhaust-gas outlet opening of an exhaust-gas outlet opening pair in each case is provided with an exhaust-gas flap that can be controlled separately from the resonator flaps.
The respective exhaust-gas outlet opening can be closed by means of the exhaust-gas flap, as a result of which further influencing of the noise emissions from the vehicle is possible. The exhaust-gas flaps can be used in driving mode, for example, to prevent the noise emissions that compromise vehicle comfort, which noise emissions can occur when the vehicle is coasting, for example. The fact that the exhaust-gas flaps are actuated independently of the resonator flaps means that it is possible for the vehicle noise emissions to be influenced over a wide application range.
According to a development of the invention, it is also provided that the common cross section of the exhaust-gas outlet openings for each exhaust-gas line is of the same size as the cross section of the exhaust-gas line concerned. In other words, this means that the total cross section of the exhaust-gas outlet openings of an exhaust-gas line is equal in size to the cross section of this exhaust-gas line. In this way, it is achieved that the flow resistance occurring in the region of the exhaust-gas outlet openings and acting against the exhaust-gas flow is not greater than the flow resistance in the exhaust-gas line, as with known exhaust-gas systems.
This means that a reduction in exhaust-gas emissions can also be achieved, as the internal combustion engine does not have to perform greater expulsion work in order to remove the exhaust gases when there is a high exhaust-gas counter pressure. The reduction in the through-flow cross section required in the case of known exhaust-gas systems for the reduction in noise emissions can therefore be dispensed with in the case of the exhaust-gas system according to the invention.
According to a development of the invention, it is also provided that the exhaust-gas system exhibits a device for the joint actuation of the flap arranged between the resonator capacity and the respective exhaust-gas line. This device may be an integral part of the engine control system and jointly control both resonator flaps, as a result of which the cost involved in supplying signal lines or control lines to the resonator flaps in the vehicle is reduced.
According to a development of the invention, it is also provided that the exhaust-gas system exhibits a device for the joint actuation of the exhaust-gas flap arranged in a respective exhaust-gas outlet opening. This device may also be an integral part of the engine control system and jointly actuate the exhaust-gas flaps, as a result of which the number of signal lines or control lines to the exhaust-gas flaps on the vehicle is in turn reduced.
According to a development of the invention, it is also provided that the exhaust-gas system has a sound-damping device provided in the through-flow direction of the exhaust-gas lines downstream of the resonator. This device for sound damping may, for example, be a rear muffler receiving the outlet opening of the respective exhaust-gas line, with which rear muffler the vehicle-specific acoustic pattern can be influenced.
According to a development of the invention, it is also provided that the resonator volume is divided by means of a partition wall into at least two partial volumes. The partial volumes can also be coupled in a controlled manner by means of an aperture passing through the partition wall, for example by means of a flap closing or opening the aperture, as a result of which the possibility is created of a further engine order being dampened in addition to the dominant engine order.
According to a development of the invention, it is also provided that the resonator has a housing body made of a plastics material, as a result of which a reduction in the dead weight of the resonator can be achieved.
Finally, it is also provided according to a development of the invention that the exhaust-gas system has a further neck opening extending in each case from the respective exhaust-gas line to the resonator volume and at least one of the existing neck openings is provided with a flap for the at least partial opening and/or closing of the neck opening in each case. In this way, a configuration is created with which a second frequency can be damped in addition to a damping frequency. When a flap is closed, the resonator dampens a first frequency by means of the neck opening which is still present and permanently open and when the flap is open the resonator also dampens the second frequency. The two frequencies may be disruptive frequencies within the meaning of humming or droning or also a disruptive frequency of this kind and the other frequency may then be a frequency which is to be lowered in respect of its level for the licensing run or the like.
The neck opening which is constantly open in this configuration for each exhaust-gas line in the direction of the resonator volume produces a bypass line with which the first disruptive frequency is permanently damped, while the second disruptive frequency can either be dampened or not dampened by opening or closing the other neck opening.
Finally, a method for operating an exhaust-gas system of a vehicle's internal combustion engine is provided according to the invention, as has been described above, and the exhaust-gas system is provided with an exhaust-gas flap in an exhaust-gas outlet opening, wherein it is provided according to the method that the exhaust-gas flap is closed when the vehicle is coasting. In this way, special disruptive frequencies occurring when the vehicle is coasting can be eliminated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.